1. Field of the Invention
The present disclosure relates to sensing technologies. More specifically, the present disclosure relates to a method and system for locating devices using a mobile sensing infrastructure.
2. Related Art
Various local or indoor positioning systems (LPS) have been developed in recent years. The signal metrics for localization include Radio Signal Strength (RSS), Angle of Arrival (AOA), Time of Arrival (TOA), and Time Difference of Arrival (TDOA). One advantage of RSS-based localization is the low cost of hardware, since most buildings are equipped with wireless local area network (WLAN) with many existing access points (AP), while the disadvantages are its low accuracy (on the order of several meters) and lack of robustness in cluttered environments, the expensive, manual processes of surveying and/or fingerprinting of the environment.
There has been a long history of using ultrasound/acoustic TOA for localization. Ultrasound/acoustic TOA-based localization has better accuracy (approximately 10 cm), but also has relatively short ranges, narrow directionality, and limited robustness in cluttered environments. It is also difficult to produce transmission and receiving sensitivities which are omnidirectional along all three dimensions.
AOA sensors are typically built using a sensor array, i.e., with several receivers arranged in a certain pattern to detect signal phase shifts between them. Therefore, AOA sensors usually cost more than other types of sensor.
Ultra wideband (UWB) technology makes precise indoor localization possible due to its long range (which can extend as far as 100 m) and its high accuracy (on the order of 15 cm). Some UWB systems use TOA or TDOA signals with homogenous nodes. That is, each node has a transmitter and a receiver, and can sense the distance from neighboring nodes within certain range. Other UWB systems may contain two types of nodes: UWB tags and sensors. Tags are UWB transmitters, do not generally have the ability to process data, and generally cannot communicate with each other. Sensors typically include an array of UWB receivers configured to obtain an AOA, consisting of yaw and pitch bearings from the receiver to a tag.
Typically, transmitters can be light and small. AOA sensors, on the other hand, are often heavier and larger. The cost of UWB tags is typically much lower than that of UWB sensors.
In conventional sensing systems, typically a set of fixed, calibrated UWB sensors in precisely known positions detect a mobile tag's signal. The host computer processes the data from UWB sensors and calculates the locations of the mobile tags. In most applications, the UWB sensors are stationary and permanently installed, while the UWB tags are mobile and tracked by the sensors whenever they are within the sensing range of the sensors. However, such a configuration typically requires a number of expensive UWB sensors, and the installation and calibration of these sensors can be very costly.